The present invention relates generally to a hydraulic shock absorber for producing an absorbing force against a shock by vortex flow of a working fluid. More specifically, the invention relates to an improvement in and related to a construction of a vortex flow chamber in the shock absorber.
The vortex flow shock absorber has been known as to be applied to a vehicle suspension and so on. Such vortex flow shock absorber has a vortex chamber in which the working fluid flows in vortex fashion to produce the absorbing force against a shock. In the vortex flow shock absorber, the absorbing force produced in response to application of the shock depends on a resistance against the fluid flow produced by the vortex in the vortex chamber.
Here, assuming the vortex chamber is sized as shown in FIG. 1, the shock absorbing force related to the size of the vortex chamber can be described by the following equations. At first, note is to be given that since the working fluid used in such kind of hydraulic shock absorber has relatively low viscosity, the fluid in the vortex chamber can be indicated as:
where
.rho.: density of the fluid, PA1 Q: unit volume of the fluid, and PA1 V.sub.r : flow velocity of the fluid at a point r. PA1 V.sub.i : flow velocity of the fluid at the inlet to the vortex chamber, and PA1 R.sub.i : radius of the vortex chamber PA1 P.sub.r : fluid pressure at the point r, and PA1 P.sub.i : fluid pressure at the inlet to the vortex chamber.
Here, since the density of the fluid P and unit volume of the fluid Q are constant, the above equation can be modified to: EQU V.sub.r.r=V.sub.i.R.sub.i ( 1)
where
According to Bernoullis theorem, the equation (1) can be modified as: EQU P.sub.r +1/2..rho..V.sub.r 2=P.sub.i +1/2..rho..V.sub.i.sup.2 ( 2)
where
From the equation (1), the fluid velocity V.sub.r at the point r is represented by: ##EQU1## Therefore, equation (2) can be modified to: ##EQU2## From the above equation (3), the fluid pressure at the outlet P.sub.o can be obtained from: ##EQU3## As apparent from the foregoing, the fluid pressure P.sub.o -P.sub.i is inversely proportional to the radius R.sub.i.sup.2 of the vortex chamber. In other word, the drop of the fluid pressure is varied depending on the radius of the vortex chamber. Therefore, it can be understood that the absorbing force against the shock corresponds to the radius of the vortex chamber.
In the meanwhile, the shock absorber is required to be small in size for convenience in application to the vehicle. Reducing the size of the shock absorber has been prevented by the limitation that the piston size must provide a sufficient absorbing force. This is caused because of the necessity of forming vortex passages for communication between the vortex chamber and the fluid chamber defined in the shock absorber. Therefore, it is necessary to take out the size limitation of the piston in order to make the shock absorber compact enough.